The invention relates to a gear, pump or motor, hereinafter gear pump, with two toothed or gear wheels rotatably mounted in a housing, the gear-tooth systems of which are in engagement with each other and separate a pressure chamber and a suction chamber or outflow chamber wherein, as a function of the angle of rotation .phi.1 of a torque-transmitting or drive gear wheel, an instantaneous volume flow V of a hydraulic medium is displaced and the meshing gear wheels have a gear ratio i.-+..phi.1/.phi.2, where .phi.2 is the angle of rotation of the non-torque transmitting, or driven, gear wheel.
Known gear pumps are constructed with at least one pair of gear wheels, consisting of two wheels with external teeth or gear wheels with external and internal teeth. A wheel with external teeth is driven and transmits the rotation to the second wheel with external and internal teeth. A difference is made between the leading and trailing edges of the gear wheels, depending on the direction of rotation. The leading edges transmit the rotation in the direction of rotation between the torque-transmitting gear wheel and the non-torque-transmitting or driven gear wheel. With a gear pump, the medium to be conveyed is conveyed in the tooth spaces from the suction chamber to the pressure chamber. The tooth edges which touch when operating, prevent backflow of the medium from the pressure chamber into the suction chamber. Because the position of the point of engagement, i.e. the points where the two tooth edges touch in the course of an engagement of the teeth, continuously changes in relation to the fixed housing, changes in the volume flow and as a result fluctuations in pressure occur in the pressure chamber in the same rhythm as the frequencies of the tooth engagements. The amplitudes of the pressure changes can attain nearly 20% of the maximum pressure in the pressure chamber. These volume or pressure fluctuations can cause trouble in the connected apparatus and result in high noise levels and thus in noise pollution of the surroundings.
In the known gear pumps, the pair of wheels of the gear-tooth system are designed such that there is a constant gear ratio between the driving and the driven toothed wheels. In this case pressure fluctuations in gear-tooth systems with play can only be reduced by keeping the distance between the instantaneous point of engagement and the pitch point as constant as possible. However, very narrow limitations are placed on this step by reason of gear-tooth system technology.
If the gear-tooth system is embodied to be free of play, it is possible in accordance with DE 34 17 832 A1 to attain an additional reduction of the pressure fluctuations also by an appropriate design of the trailing edges of the gear-tooth system, because then the point of engagement as the sealing threshold between the pressure chamber and the suction chamber is located not only at the leading edges, but at times also at the trailing edges of the two wheels. In a pump free of play with the conventional involute profile of the leading and trailing edges there is necessarily a reduction of the volume or pressure pulsation to one fourth, because the length of the engagement path which determines the pressure pulsation has been halved. An additional, but considerably smaller reduction of the length of the engagement path and thus of the volume or pressure pulsations, can be achieved by appropriately designed trailing edges. The leading edges continue to determine the kinematics of the pump. The leading edge profile is embodied as in the known gear pumps in which the trailing edge profile is symmetrical with the leading edge profile and without effect on the volume or pressure pulsation. With the proposed gear-tooth system free of play, the leading edge profile and the trailing edge profile of the torque-transmitting and the non-torque-transmitting wheels are the same. The gear-tooth system profiles are called simply symmetrical. Because the leading edge profile corresponds to the customary gear-tooth system profiles, no changes occur in the kinematics of the proposed gear pump with respect to those known, i.e. both toothed pump wheels have a constant angular velocity. The volume or pressure pulsation can only be reduced, but not prevented, by freedom of play and trailing edge design, because the length of the engagement path cannot be zero. Pumps free of play will not be realized in practice because thermal and elastic deformation as well as tolerances as a result of manufacturing alway require sufficient edge play.
In DE 24 39 358 A1 it is proposed to connect a gear, which compensates for the uneveness of the conveyed flow, upstream or downstream of hydrostatic pumps or motors having a displacement device which generates or receives a periodic conveyed flow. The proposed gear is intended to generate an uneven angular speed at the torque-transmitting shaft of the pump and in this way cancel the pulsation of the conveyed flow. The downstream gear is intended to generate an even angular speed on the driven gear shaft of the motor. It is furthermore proposed to embody the gear as a toothed-wheel gear. The proposed solution uses unmodified known displacement machines, i.e. the constant gear ratio usual with the gear pump and thus its kinematics are retained. The proposed solution cannot be employed in practice because of the occurring inertia forces, the loads and noise appearing because of that and for reasons of economy.